Well in the colonial days and likely before the anvil was basically Iron with some steel blacksmith welded on the face. I would think the first thing to do is hit it with a grinder and see whether the thing is steel or iron.
you might experiment with putting the anvil in the vertical position and clamping a piece of copper to the good face and filling in with weld a quarter of an inch or so at a time letting the weld collapse against the copper.
or you could put it on a milling machine and dress up the rough face so as to just weld a plate in the low spot. just weld around the edge and at the seam. or figure out how to blacksmith weld.
I will post some pictures soon. No, the rest is attached solidly. It is not an uncommon failure of anvils with tops forge welded on them. The anvil looks sort of continental to me, maybe it is German. It has little flowers deep stamped on it.
I was going to leave this one alone, since its such a complex subject, but------ I know a guy who did the following:
Plane or mill the whole hard plate off the anvil. (can be done with carbide tooling).
Dovetail the upper surface of what's left.
Get a new piece of tool steel and dovetail it to match.
Heat the plate up and drive it into place.
That's what he told me. There are a couple of pieces of the story missing, though. He must have needed to harden and temper the plate after machining. If so, the material must have been able to stand the heat used to expand it without loosing the temper.
I suppose, that if they guy could have settled for 4140 and had a pretty powerful Mill, he could have used hard or half hard material and machined it in that state. Then he'd not need to do you heat treating. He could reheat to around 450°F or so for installing without destroying the hardness.
This is what they guys around here do. Personally, I'd rather hit my fingers with a hammer "because it feels so good when you quit" than do it, but you get to decide. I only surface grind the anvils for them when they are done.
The SP track welders were told to lay down a thick bed of 4140 or
4340(?) using 1/4" welding rod and a ~3/4" rose bud before using the arc welder to finish building up the rail head or more likely a frog point.
I knew a track welder (Hey Fred French!;) that could make it work by going directly to the arc welder. Some others were having trouble doing that so the new rules came down and Fred did follow orders. ;)
Alvin in AZ ps- Now, if dumb ol' Fred would just find this, he'd explain the friggin details to us. ;)
Sounds like putting the OA bead on first would be a good way to preheat the heck out of the rail. A friend of mine talks about using two OA torches with #9 or #10 tips to build up frogs. He didn't like the arc welder very much when it came along. Besides, he said, it came on a rail car of its own and you had to wait until the one arc welder that the railroad owned showed up.